Mechanical properties and thermal shock behaviour of alumina–mullite–zirconia and alumina–mullite refractory materials by slip casting

Strength and modulus values of slip-cast alumina–mullite–zirconia and alumina-mullite refractories have been determined as a function of quench temperature by air and water quenching. The resistance to fracture initiation and propagation caused by the thermal stresses was increased with the addition of zircon, as supported by the R and Rst parameters. There was no catastrophic decline in strength on thermal shock at high temperature or with repeated cycling, where a large proportion of intergranular fracture in the fracture surfaces was observed. There was ∼50% loss of strength after the 1st cycle, and further cycling did not markedly change the retained strength of the material to the 40th cycle. The inevitable cracking occurred after thermal shock testing was kept below the critical crack length due to the transformation toughening effect of zirconia, thus maintaining a high degree of integrity, associated with the high values of K1c and γi.